The dipterous fauna in 32 mines, 5 caves and some other cave systems in southern Norway has been studied with regard to species composition and periodicity. Some 20 000 specimens belonging to 80 species in 18 families were recorded. Mycetophilidae (95.0% ), Culicidae (3.2%) and Heleomyzidae (1.3%), dominated. With the exception of Speolepta leptogaster (Winnertz, 1863) (Mycetophilidae), a possible troglophile, all species must be regarded as trogloxenes, most of them habitual trogloxenes inhabiting cave systems for hibernation. Some differences regarding species composition in dif6ferent cave systems and between western and eastem Norway were demonstrated. Seasonal occurrence and sex-ratios reflect different life cycle strategies and seasonal adaptations among the habitual trogloxenes: hibernators, (Mycetophilidae, Culicidae), aestivators (Limoniidae, Bolitophilidae), species which seek cave systems independent of sex and season (Heleomyzidae, Trichoceridae), and opportunists (Chironomidae, Phoridae?, Dixidae?). Species belonging to other families are most likely accidental trogloxenes.